Api 6a718 free download

Sometimes a one-time extension of up to two years will be added to this review cycle. This publication will no longer be in effect ve years after its publication date as an operative API standard or, where an extension has been granted, upon republication.

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Also, the revised Standard has some areas in at all orders of compressor run speed. These forces cause the the specification that require interpretation by engineer- compressor cylinder to move away from, and toward, the ing service providers. This motion is commonly called frame Part II of this article expands on some of these impacts to stretch or cylinder stretch. See Figure 1. Cylinder stretch motion can cause high-frequency vibra- tions on the bottles and piping close to the compressor1.

Beta, as well as www. During a DA3 study, the vibra- help decide which study scope is recommended. These forces can be a significant source of excitation at all orders of compressor run speed. Mechanical Design Goal as shown in Figure 2. This figure illustrates that the forces in a variable speed Minimum MNF for Compressor System unit red arrows will occur across a wide frequency range, based on different run speeds making it difficult to design a scrubber with an MNF be- tween 1x and 2x run speed.

Moving the MNF above 2. In general, the piping or vessels must be much stiffer 20 48 Hz than in slower-speed units. Early communication between 30 72 Hz the compressor packager, owner and vibration consultant is necessary to ensure acceptable vessel and skid designs. For high-speed analysis should be conducted.

Table 2 below explains why. A compressor me- This separation margin requirement can create problems. Skid pressure pulsations and the cylinder stretch forces. API has developed force guidelines proven to result sign can dramatically affect MNFs, vessel fabrication draw- in successful designs and controlling vibrations from pul- ings must also be available at this time. Modeling If the cylinder stretch forces are above a certain level, a techniques must be field verified.

The second step in assessing frequencies. Inter-tuning can be an option if approved by the cylinder stretch forces is evaluating the mode shapes the owner and packager2.

This involves input from the owner on the Confusion in Quoting DA3 Studies amount of vibration risk that is acceptable and avoids costly As discussed in Part I of this series, the DA3 may require changes later.

This creates confusion in the quotation API 5th Edition gives some general direction for per- phase, because it is uncertain if the forced response analy- forming simulations and modeling. However, accurate sis will be required and what the associated cost will be of analysis requires that specific details and techniques be these contingencies. Also, the scope of the forced response used. Different levels of quality exist in the industry buyer study may not be apparent during the quotation phase.

Following, are four key areas that affect accuracy: Depending on the situation, the scope of the study, or stud- ies, could be small, or quite large. There are two possible Pulsation Analysis — Numerous technical articles docu- forced response studies to consider.

In addition to better accuracy, TD algorithms can Study — Step 3b1 is typically required for medium- to calculate both static and dynamic pressure drop. Dynamic pressure drop calcu- low 1. For scrubbers, the most important factor in the FEA packages for the following two reasons: the pulsation de- model is the boundary condition assumption between the scrubber and the skid. Figure 3 illustrates the details needed for accurate analysis mounting plate, bolts, beams and local skid construction.

High error can mean high vi- construction. Compressor Stiffness Assumptions — Because of high gas forces, the compressor frame cannot be considered a rigid body for dynamic studies, even when mounted on concrete. Accurate stiffness assumptions are required when modeling the compressor MNFs DA3, Step 3a and forced response analysis of the compressor and bottles Step 3b1. The im- proved accuracy can reduce the need for costly mechanical supports and braces4. All mechanical models must employ 3-D FEA techniques to calculate shell flexibility accurately.

Simplified assump- tions are not valid. Option: for projects requiring high accuracy, the mechanical analysis should include the compressor frame in the mechanical model.

Tips Given the confusion on forced response studies, we recommend the following three tips for obtain- ing DA3 study quotations from vibration consultants: Obtain a firm quote on DA3, Step 3a. Compare suppliers based on this price.

Determine likelihood of forced response analysis Step 3b 1 and 2. Supply optional prices for these studies if required. Complete a Risk Rating Assessment3 for the com- pressor. This is a good practice for defining the risk parameters with the unit. Early involvement between the packager and vibra- tion consultant is recommended to discuss pulsation and mechanical design options early in the project avoids costly changes for the owner later.

This FEA model of a compressor frame illustrates exaggerated local flexibility. Footnotes 1 Refer to technical article: Cylinder Stretch as a sign will typically reduce pulsation forces to low levels; and Source of Vibration in Reciprocating Compressors, , the mechanical analysis will avoid resonance at the first and available as a free download fromwww. For example, de- load from www. Mechanical Analysis, available as a free download from Another example is a project involving an existing facility its website www.

Summary Specifications to Ensure an Effective Pulsation and Vibration Study— The following specifications will ensure accurate pulsa- tion and vibration analysis, improved reliability for own- ers , less warranty costs for packagers , and a level playing field when quoting on projects for vibration consultants. Include TD and FD simulations in the pulsation analysis. The report must contain dynamic pressure drop and TD plots of key forces and pressure pulsations for all condi- tions and all frequencies under Hz.

Determine the appropriate compressor stiffness assump- tion based on field-proven results or detailed computer simulations. Mechanical models shall not assume the com- Recommendations for Reducing Compressor Total pressor frame is a rigid support. A comprehensive review Life Cost and Improving System Performance of the compressor skid and foundation design must be con- The 5th Edition of API the Standard was officially re- ducted by experienced analysts to assess the design and leased in December The Standard specifies the mini- determine if skid and foundation analysis is required.

It does however, encourage com- Employ 3-D FEA analysis in mechanical models of pulsa- pressor designs to be more energy efficient. The updated 5th tion bottles to calculate shell flexibility. Improving efficiency and reducing the total life cost can be accomplished through different points of view.

Three ar- eas that can result in significant savings are: 1. Pulsation control devices introduce pressure drop into the system. Reducing pressure drop results in in- creased capacity, or reduced fuel costs. Increased capacity generates millions of dollars per year in incremental throughput. Fuel savings can generate hundreds of thou- sands of dollars per year in savings. An overly conservative design can have significant cost penalties.

This information is provided by the pulsation analysis. Note 3. Over the life of a compressor, the field infrastructure that the pulsation analysis must employ proven Time may change the operating parameters of the unit beyond Domain algorithms to obtain accurate total pressure drop re- those anticipated during the initial design.